Calculate your physical, emotional and intellectual cycles from your birth date and see the chart for the 30 days around today.
Biorhythm theory, created by Berlin physician Wilhelm Fliess and Vienna psychologist Hermann Swoboda in the late 19th century and later extended in the 1920s by engineering professor Alfred Teltscher, proposes that three sine-wave cycles start on your birth date and repeat forever: a 23-day physical cycle, a 28-day emotional cycle and a 33-day intellectual cycle. Each cycle swings between -100% and +100% following the formula sine(2π x days lived / cycle length), crossing zero on the so-called "critical days," when tradition says that aspect turns more unstable. This tool computes all three cycles in your browser from your birth date (and any other date you want to check) and draws the chart for the 30 days before and after the chosen date. Worth stressing: despite being popular ever since businessman George Thommen and, especially, writer Bernard Gittelson sold millions of books on the subject in the 1970s, the theory has never held up under controlled testing. We treat the result as curiosity and self-reflection, not a real prediction.
All three cycles use the same formula, only the period number changes: value = sine(2π x days lived / period). "Days lived" is simply how many whole days have passed between your birth date and the date you are checking, counted from midnight to midnight. Sine always produces a number between -1 and +1, which we multiply by 100 to turn into a percentage between -100% and +100%.
Because the three periods (23, 28 and 33 days) share no small common multiple, the three cycles rarely line up at the same time, which is why the chart tends to look "out of sync": each line rises and falls at its own pace, crossing zero (that cycle's "critical day") whenever the days-lived count is a multiple of half the period.
The idea began with Wilhelm Fliess, a Berlin ear-nose-throat physician and friend of Sigmund Freud, who in the late 19th century believed he had found 23- and 28-day rhythms behind births, deaths and other events, labeling them the "male" and "female" cycle (the latter tied to the menstrual cycle). Around 1904, Vienna psychologist Hermann Swoboda reached similar conclusions independently, and the two publicly feuded over who had the idea first. Swoboda even sued Fliess for defamation and lost.
In the 1920s, Austrian engineering professor Alfred Teltscher added the third cycle, 33 days long, after noticing, with no experimental control, that his students' performance seemed to follow a rhythmic pattern. The theory stayed niche until the 1960s and 1970s, when Swiss-American businessman George Thommen and, especially, writer Bernard Gittelson turned it into a commercial phenomenon in the United States with a series of best-selling books, including "Biorhythm: A Personal Science".
Psychologist Terence Hines reviewed the literature twice: first in 1979, in the skeptic magazine Skeptical Inquirer, and later, more comprehensively, in 1998, in the academic journal Psychological Reports ("Comprehensive Review of Biorhythm Theory," volume 83, issue 1, pages 19 to 64). In total, he examined 134 biorhythm studies: 99 found no correlation whatsoever between the cycles and the tested variables (accidents, athletic performance, school grades, deaths), and the 35 that reported some support for the theory contained methodological or statistical errors that explained the result.
Hines' conclusion, now widely accepted, is that the theory "is not valid": whatever correlation shows up in isolated studies falls within what chance alone would explain, not what a real biological cycle would produce. That is why biorhythm ended up on the list of pseudosciences, alongside astrology and numerology. This tool reproduces the classic formula with mathematical accuracy, but treats the result as entertainment and self-reflection, never as a diagnosis or a prediction.
Paste the code into your HTML and the tool shows up on your page, without J-Kit's navigation and ads. It still runs in the browser of whoever visits your site.
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src="https://jkit.tools/embed/en-US/biorhythm-calculator"
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></iframe>These references help contextualize formulas, standards, APIs and limitations used on this page. They do not replace professional validation when a result has legal, financial, medical or operational impact.
It is a popular theory, not a real biological measurement, that claims three aspects of life (body, emotions and mind) follow fixed sine-wave cycles, starting at birth and never changing period. This calculator reproduces the classic formula purely for curiosity and entertainment.
By default we show today, but you can pick any other date, past or future, to see how the three cycles would look on that day.
Enter your birth date to see the three cycles.
Your birth date and reference date stay in your browser and are never sent to any server.